Technical Field
The present disclosure relates to a laminate-type power storage element that houses a power generation element in an exterior body formed of laminated films and a method of manufacturing the same.
Related Art
A laminate-type power storage element houses a flat plate-shaped electrode body including a sheet-shaped positive electrode and a negative electrode in a flat-bag-shaped exterior body formed of laminated films. The laminate-type power storage element, which is appropriate for downsizing and thinning, is used as a power supply for an extremely thin electronic device (hereinafter, a thin electronic device) or similar device that incorporates a power supply, such as an IC card with a one-time password function and a display, an IC card with display, a tag, and a token (one-time password generator).
FIG. 1A and FIG. 1B illustrate an exemplary laminate-type power storage element 101. The laminate-type power storage element 101 exemplified in FIG. 1A and FIG. 1B is a lithium primary battery using a nonaqueous electrolyte. FIG. 1A is an external view of the laminate-type power storage element 101. FIG. 1B is an exploded perspective view illustrating an exemplary internal structure of the laminate-type power storage element 101.
As illustrated in FIG. 1A, the laminate-type power storage element 101 has a flat plate-shaped appearance. An exterior body 11 formed of laminated films 11a and 11b shaped into a flat rectangular bag internally seals a power generating element. In the laminate-type power storage element 101 illustrated in FIG. 1A and FIG. 1B, a positive electrode terminal plate 23 and a negative electrode terminal plate 33 are guided to outside from a predetermined margin 13 (hereinafter referred to as a terminal lead margin 13) of the rectangular exterior body 11.
Next, the following describes a structure of the laminate-type power storage element 101 with reference to FIG. 1B. FIG. 1B hatches some members and sites for easy distinction from other members and sites. As illustrated in FIG. 1B, the exterior body 11 internally seals an electrode body 10 together with electrolyte. The electrode body 10 is formed by laminating a sheet-shaped positive electrode 20 and a sheet-shaped negative electrode 30 via a separator 40.
The positive electrode 20 is formed by disposing a positive electrode material 22 containing a positive-electrode active material over one principal surface of a positive electrode current collector 21 made of a metal plate or a metal foil. The negative electrode 30 is formed by disposing a negative electrode material 32 containing a negative-electrode active material over one principal surface of a negative electrode current collector 31 made of a metal plate, a metal foil, or a similar material. The electrode body 10 is configured by laminating and press-bonding the positive electrode 20 and the negative electrode 30 such that the positive electrode material 22 and the negative electrode material 32 (hereinafter referred to as the electrode materials 22 and 32 as a whole) are opposed via the separator 40.
The exterior body 11 is configured by welding peripheral edge regions 12, which are hatched or indicated by the dotted line frame in FIG. 1B, of two rectangular aluminum laminated films (11a and 11b), which are stacked to one another, by thermocompression bonding to seal the inside. As is well-known, the laminated films (11a and 11b) have a structure where one or more resin layers are laminated on front and back of a metal foil (aluminum foil, stainless steel foil) serving as a base material. Furthermore, generally, the laminated films (11a and 11b) have a structure where a protecting layer made of, for example, a polyamide resin is laminated on a front surface, which will be an outer surface of the exterior body 11, and an adhesive layer with thermal weldability made of, for example, a polypropylene is laminated on a back surface, which will be an inner surface of the exterior body 11.
The positive electrode current collector 21 on which the positive electrode material 22 is laminated is electrically coupled to the positive electrode terminal plate 23. The negative electrode current collector 31 on which the negative electrode material 32 is laminated is electrically coupled to the negative electrode terminal plate 33. Then, the positive electrode terminal plate 23 and the negative electrode terminal plate 33 (hereinafter referred to as the electrode terminal plates (23 and 33) as a whole) are guided outside of the exterior body 11, which is in a sealing state.
Therefore, at a part to which the electrode terminal plates (23 and 33) are guided at the terminal lead margin 13 of the exterior body 11, the adhesive layers of the laminated films (11a and 11b) are not welded to one another. Thus, an adhesive strength between the electrode terminal plates (23 and 33) and the laminated films (11a and 11b) are possibly not sufficiently ensured.
At the terminal lead margin 13, it is difficult to interpose the adhesive layers in a melted state over a thickness direction of the electrode terminal plates (23 and 33). Thus, this terminal lead margin 13 is possibly not sufficiently sealed to reduce a waterproof performance.
Therefore, the laminate-type power storage element 101 has a structure for surely sealing the terminal lead margin 13 of the exterior body 11. A sealing method of the terminal lead margin 13 includes a method using tab leads 50 as the electrode terminal plates (23 and 33) and a method that mounts strip-shaped metal foils or metal plates (hereinafter referred to as terminal leads 51) to the positive electrode current collector 21 and the negative electrode current collector 31 (hereinafter referred to as the electrode current collectors (21 and 31) as a whole) to use these terminal leads 51 directly as the electrode terminal plates (23 and 33).
FIG. 1B illustrates the method using the tab leads 50. The electrode terminal plates (23 and 33) constituted of the tab leads 50 are coupled to the positive electrode current collector 21 and the negative electrode current collector 31 respectively. The tab lead 50, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2008-192451, has a structure where a sealing material (hereinafter, a tab film 52) made of insulating resin is bonded on an extension of the strip-shaped terminal lead 51 made of a metal plate or a metal foil that is substantively the electrode terminal plate (23 or 33) so as to sandwich this terminal lead 51.
The terminal leads 51 each have one end portion 53 exposed to outside of the exterior body 11, and the other end portion coupled to parts of the positive electrode current collector 21 and the negative electrode current collector 31 by a method such as ultrasonic welding. Needless to say, separate strip-shaped metal plates or metal foils may be mounted to the positive electrode current collector 21 and the negative electrode current collector 31 to further couple the tab leads 50 to these metal plates or metal foils. Then, when the flat-bag-shaped exterior body 11 is formed by thermocompression-bonding the peripheral edge regions 12 of the laminated films (11a and 11b) opposed to one another, the tab films 52 of the tab leads 50 are thermally welded with the laminated films (11a and 11b) at the terminal lead margin 13 of the peripheral edge region 12 of the exterior body 11. Accordingly, at this terminal lead margin 13, the tab films 52 welded to the terminal leads 51 are welded to the adhesive layers of the laminated films (11a and 11b).
On the other hand, the method using the terminal leads 51 directly as the electrode terminal plates (23 and 33) without the tab leads 50 further includes a method that mounts separate terminal leads 51 to the positive electrode current collector 21 and the negative electrode current collector 31, and a method that integratedly forms strip-shaped convex portions corresponding to the terminal leads 51 on the respective positive electrode current collector 21 and negative electrode current collector 31 to take these convex portions as the electrode terminal plates (23 and 33).
FIG. 2A and FIG. 2B illustrate exploded perspective views of laminate-type power storage elements (102 and 103) that employ a method without the tab leads 50. FIG. 2A illustrates the laminate-type power storage element 102 corresponding to the method that mounts the electrode terminal plates (23 and 33) as the separate terminal leads 51 to the positive electrode current collector 21 and the negative electrode current collector 31.
FIG. 2B illustrates the laminate-type power storage element 103 that disposes convex portions (24 and 34) that double as the electrode terminal plates (23 and 33) on the positive electrode current collector 21 and the negative electrode current collector 31. Then, as illustrated in FIG. 2A and FIG. 2B, the laminate-type power storage elements (102 and 103), which have employed the method without the tab leads 50, employ a method that seals the terminal lead margin 13 using strip-shaped tab films (14a and 14b) instead of the tab leads 50.
Then, in this method, in the peripheral edge region 12 of the exterior body 11, the strip-shaped tab films (14a and 14b) are bonded to the terminal lead margin 13 by thermocompression bonding, in a state where the strip-shaped tab films (14a and 14b) are preliminarily welded to the back surfaces of the laminated films (11a and 11b). Then, the exterior body 11 is shaped by thermocompression-bonding the peripheral edge regions 12 of the laminated films (11a and 11b).
That is, for the laminated films (11a and 11b) opposed to one another, the laminated films (11a and 11b) are bonded to one another via these strip-shaped tab films (14a and 14b) at the terminal lead margin 13.
Non-Patent Literature (FDK CORPORATION, “Thin Type Primary Lithium Batteries, Internet <URL: http://www.fdk.co.jp/battery/lithium/lithium_thin.html>) and Japanese Unexamined Patent Application Publication No. 2006-281613 describe such technique.
As described above, the laminate-type power storage elements 101, 102, and 103 have the structure where the electrode terminal plates (23 and 33) are guided from the flat bag-shaped exterior body 11 by thermocompression-bonding the opposed laminated films (11a and 11b) one another. Then, the method that seals the terminal lead margin 13 of the exterior body 11 basically includes the method using the tab leads 50 (hereinafter referred to as a tab lead method) and the method using the strip-shaped tab films (14a and 14b) (hereinafter referred to as a tab film method).
In the current situation, the tab lead method is a mainstream. However, in this method, the terminal leads 51 of the tab leads 50 are welded to the electrode current collectors (21 and 31) by ultrasonic welding, thus increasing man-hours in assembling the laminate-type power storage element 101, and an expensive ultrasonic welding machine is also required, thus increasing a production cost of the laminate-type power storage element 101.
Furthermore, the tab lead 50, which is a required member, is a member sold as an industrial product manufactured separately from the laminate-type power storage element 101, thus also increasing a member cost in the tab lead method compared with the tab film method.
On the other hand, the tab film method does not require the tab lead 50, which is an expensive member, and is also applicable to the electrode body 10 having a structure where the electrode terminal plates (23 and 33) and the electrode current collectors (21 and 31) are preliminarily integrated. Accordingly, the tab film method overwhelmingly has an advantage in price reduction and versatility compared with the tab lead method. Then, when the laminate-type power storage elements appropriate for downsizing and thinning are provided for use in, for example, IC cards provided in large amounts, and extremely inexpensively, and in some cases, charge-free, the price reduction is required as an extremely important matter for the laminate-type power storage element. Accordingly, it is expected that the tab-film-method laminate-type power storage element will be a mainstream in the future.
Then, when the inventor has examined reliability of the tab-film-method laminate-type power storage element, the inventor has found the reliability decreases caused by a structure of the laminated film. This will be described with reference to FIG. 3.
FIG. 3 is a side view of the laminate-type power storage element 102 illustrated in FIG. 2A in a state incorporated in a thin electronic device when being viewed from a thickness direction of the laminate-type power storage element 102.
As illustrated in FIG. 3, when the laminate-type power storage element 102 is incorporated in the thin electronic device, regions projecting outside the exterior body 11 at the electrode terminal plates (23 and 33) (hereinafter referred to as electrode terminal portions (25 and 35)) are coupled to a circuit board 100. At this time, for example, the electrode terminal portions (25 and 35) possibly bend into crank shapes. Then, when base ends (26 and 36) sides of the respective electrode terminal portions (25 and 35) of the positive electrode 20 and the negative electrode 30 bend taking the terminal lead margin 13 as a fulcrum, the electrode terminal plates (23 and 33) possibly contact the metal foils exposed on cutting surfaces 11c of the laminated films (11a and 11b) to short-circuit the positive electrode 20 and the negative electrode 30. It is considered to prevent the short circuit by sticking an insulating tape (hereinafter referred to as a protective tape) that protects the cutting surfaces 11c of the laminated films (11a and 11b). However, this protective tape inhibits thinning of the laminate-type power storage element 102, and also inhibits the cost reduction due to a member cost of the protective tape and a process addition for sticking the protective tape.